Thiophenes as Potential Contributors to the Formation of Organosulfates and Sulfonates in Urban Atmospheric Aerosols

Organosulfates and sulfonates (OSs) are important components of atmospheric aerosols and may have implications for climate and human health. Despite extensive research on the formation of OSs, the origins of over 50% of OSs mass in ambient aerosols remain unknown. Here, we demonstrate that thiophenes, emitted from multiple anthropogenic sources (e.g., coke fuel production) and contributing ∼44 Gg of sulfur emissions annually, are previously unrecognized potential OSs precursors in the urban atmosphere. For instance, C₅H₈O₅S and C₄H₆O₅S were previously detected in the urban atmosphere but their origins were unknown. Our study identified these two OSs as products of the nighttime oxidation of 2-methylthiophene, suggesting that 2-methylthiophene may act as a potential precursor for C₅H₈O₅S and C₄H₆O₅S in ambient aerosols. Both 2-methylthiophene and benzothiophene can lead to the formation of OSs that were solely attributed to the photooxidation of isoprene and naphthalenes in prior field studies (e.g., C₅H₈O₇S and C₇H₆O₄S). We highlight that the nighttime oxidation of thiophenes can directly produce gaseous oxygenated organosulfur compounds without external sulfur (e.g., sulfate), which is a previously unrecognized pathway that could contribute to the OSs formation in urban atmospheric aerosols.